Luminous electric discharge tube



lli

lill

Patented ug. 6, 1929.

UNITED STATES PATENT oEFicE.- l miami rnurcorrn, or nautisme, einem i .Appnation med oqtgber 2, 1928, Serial/No. 139,231, and in Belgium March 9, 1928.

The present invention relates to the industrial manufacture of luminous electric discharge tubes filled with rare gas.

The industrial manufacture of such luminous tubes filled with rare gas such as neon or helium meets various impediments, especially when it is sought to obtain tubes of high luminosity together with long duration.

lndeed, the luminosity is proportional tno the amperage. to Which the luminous tube is subjected, While its lite is inversely proportional thereto.

'lhese two requirements may, however., be rendered compatible by bringing particular care in the manufacture of the tubes.

lt is indeed known that gases such as neon and helium are more luminous and better conductors then hydrogen, nitrogen, carbonio acid or oxygen. therefore. be taken to eliminate the lastnamed ases from the glass and the metals in Which t ey are occluded before any introduction oiE rare gas, which has itselitl to be puriiied.

llt should be avoided that after a lite of more or less duration ot the tube the neon or the helium maybe absorbed by the electrodes, as thiscvvould reduce the conductibility of the luminous tube and necessitate a higher amperage.

New, it is known that, the more the ain'- pei'age is increased, the more the neon or the helium is absorbed during the cooling of the electrodes, ot 'which the metal becomes heated under the induence of the passage ot the electric current. A

ln order to minimize this increase ot teniperature ol the metal and to reduce the consequent absorption, it has been suggested to increase the area of the electrodes, through which the current enters. y y,

'lhe present invention consists in the construction ot an improved luminous electric .discharge tube, lled with rare gas, the tube being provided, at one or at each end, With a I' plurality oit substantially identical electrodes, connected in parallel, and each made olI a spirally Wound plate ot metal having a high melting point, so that the natural ditilerence 'between the electric resistances ot the different electrodes will bring an alternation in the electric discharges for the different electrodes. a 'llhe general process of manutacturing said tubes will be: characterized by the elimination ofthe gases occhided iii the Particular care should' electrodes by exposing them to electric discharges in aseparate tube filled with nitrogen; the purified electrodes will be mounted in branches of the tubes, said branchesto be fused to the tubes; the Vluminous tube itself will be purified by means of electric dischai'gesin a nitrogen filling with 'subsequent absorption of residual gases, by means ot an auxiliary shunteol electrode ot palladium, the tube so prepared to be emptied and dlled with rare gas previously purified.

The invention will now be described with reference to the accom anying drawings.

Fig. l shovvs a tube lliaving four, and Fig.. 2 a tube having three electrodes. Fi' 3 represents on a larger scale the disposition ot one pair of electrodes at one end ol a tube, and Fig. l is a diagram for illustrating the process of purification ot the electrodes.

The. tubes or our invention comprise a t .plurality ot electrodes l, Q4, in arallel, mounted at one or at each end of t e luminoustube a. These electrodes are of the saine kind, present an equal area and are situated at equal distances the one from the other. The tube b of Fig. 2 is provided at one end with two electrodes l, 2 and at the other end with one electrode 3. Said electrodes are made of a metal having a high melting point. Molybdenum or tungsten in the shape or thin plates will e@ pecially be suitable. The' atomical constitu tion of 4those metals, Whereirom occluded gases lcan be readily eliminated, makes tbenr also practically less permeable than any other to gases with Which they are brought in contact.

Those metal plates are spirally l*Wound as designed in lfig. 3, in order that `the electrodeniay be of a reduced volume While it of expansion Without exerting any strain upon its support. fThe electrode is mounted, as illustrated, in a glass cup l making part of the inner Wall of the luminous tube, which 16W tube alternatively by one and by the other 1w electrode for each end of the tube in a Way as will be described hereafter.

In order to explain the action of the multiple electrodes, it should be noted that rare gas is absorbed by the electrodes at the mo- 1w dll till

titl

dll

mi keeps the necessary resiliency and capacity ment when the latter are cooling. From this experimental statement, it results that the more the electrodes are heated, the more they.

will absorb rare gas on cooling and the object of the present invention is to reduce at a minimum said heating objectionable for the life of the tube. v

Considering the case of two electrodes at each end of the tube a, the current is supplied to the ends of said tube through the double electrodes 1 and 2, connected t o the conductors 5 5, 6 6. As it is practically impossible to construct two electrodes strictly identical as to the resistance they will offer to the passage of the current, this by reason of lack of atomical liomogeiieousness of their metal, one of the two electrodes, for instance 1, will always present at the moment of priming a resistance inferior to that of the other electrode 2. Priming will thus take place upon the first electrode l and the same fact is realized at the other end of the tube a.

After some moments of Working, the electrode 1 upon which priming took place will become heated and offer more resistance to lt is indeedthe passage of the current. known that the conductivity f a metal is inversely proportional to its temperature. At this moment, the electrode 2 Which` remained cool will automatically take the current. Obviously, the other end of the tube will present an identical phenomenon.

Then the electrode l or 2 is in action, the

i electrode 2 or 1 is cooling and this the more rapidly as they are not brought to a very considerable temperature before being relieved by the other electrode.

If for some reason the tube will have to produce a luminosity superior to the normal one, as by dense fog, the working voltage of the tube will only have to be increased.

In such cases the electrodes becoming hotter, there will arrive a moment where their respective i'esistances tend to balance. This critical point being attained, it appears as an experimental fact that the current passes through the electrodes, in parallel, alternatively and at a rate of 25 times per second, if the frequency of the supply current is of 50. Indeed, if the resistance of the two electrodes becomes identical at a given moment, the passage of the current in one of them during one half period will be sufficient to break this balance and the two electrodes will set to work alternatively.

It should be observed that such device regulates the normal working of the tube during its whole eXistence,by the fact that the alternation becomes the more rapid as the pressure of the gas in the tube is decreasing. Indeed, if the tube is originally adjusted for a gas pressure y at the .current intensity w, any working of the tube will provoke an absorption of a small quantity of the gas and this brings forth a decrease of pressure.

This diminution of pressure involves automatically an increase of the current intensity. Any increase of intensity will bring forth a more rapid rupture of balance for the temperatures of the parallel electrodes, with the result that more rapid alternation will arise.

It can thus be easily understood that the device has a regulating and limiting function for the temperature of the electrodes. This limitation of the heating of the electrodes to a minimum will oll'er the advantage of an extension of life of the tube.

lt is however necessary, before mounting definitely the electrodes in the luminous tube, to eliminate carefully the gases occludcd in them. Such process will be described hereafter with i-efercnce to the diagram of F ig. 4.

The electrodes l and 2 are placed at the ends of a separate glass tube 7 of relatively great diameter and they are connected each to the secondary winding of a transformer 8 whereof the primary winding is under control of a self inductance 9 having a movable core for the regulation of the current intensity and tension. The glass casing 7 communicates on the one side with a vacuum pump by means of the conduit 12, on the other side with a nitrogen generator, by means of the conduit 10; said conduits 10 and 12 comprise a sluice device formed by means of cocks, in order to allow regulation of the internal pressure of the casing 7 by successive charging or discharging. A quantity of potassium is located at l1 in the conduit l2, on the way to the Vacuum pump, said potassium being necessary for the absorption of gases by contact, etc.

The process consists in making a partial vacuum in the casing 7, and introducing a nitrogen atmosphere supplied through 10 while keeping an appropriate pressure to allow priming of the passage of a current of progressive intensity until complete blackening of the walls of the tube occui's. The regulation of this progressive intensity can be readily operated by the combination of the transformer with the self inductance 9, as, once the passage of the current is started in the tube 7, the ionization of the atmosphere will involve a decrease of resistance to the passage of the current, so that the intensity of the latter may increase for a diminution of the tension.

The nitrogen atmosphere will be renewed several times and any trace of occluded gases will thus be eliminated from vthe electrodes; such, are the hydrogen and oxygen, which willeombine themselves with the nitrogen to form gases readily removable. Under the influence of the electric discharges, the nitrogen and hydrogen will combine to form ammonia and the nitrogen and oxygen to form nitrogen peroxide, both to be readily absorbed by the reserve of potassium 11.

It can be observed that the purification of r`the electrodes is completed when the spectral Before the introduction of they rare gas in' the tube, it must be observed that the bad electric conductivity of hydrogen and oxygen which may remain in the tube does not allow the introduction ofthe rare gas under an elevated pressure; further, the least trace of hydrogen could afterwards provoke a superheating of the electrodes. It is thus necessary to eliminate completely thehydrogen and oxygen of the prepared tube and this v operation is performed by passing a new charge of nitrogen in the luminous tube under electric discharges in the same manner as has been` described for the operation of purification of the electrodes 1 and 2. When the last gases are eliminated out of the tube, the most complete vacuum is made in the same prepared tube and the rare gas, such as neonor helium is admitted. For the elimination of hydrogen and oxygenthat may still be present in the prepared tube, but before the introduction of the rare gas, an auxiliary electrode could be branched upon the tube, filled with a nitrogen atmosphere, said auxiliary electrode being formed of a plate of palladium of any size, automatically heated by the passage of the electric current; this `metal will absorb rapidly the oxygen and hydrogen, as it has the property to do so.

The other residual gases will be progressively absorbed by the passage of the electric current, `according to a technique similar to that of the formation of Crookes tubes or vapour of mercury lamps.

The nitrogen in particular will be eliminated by the addition in the same conditions as the palladium or a tungsten .filament brought to a red glow by mea-ns of a small voltage reducing transformer branched directly onto a 11G-volt circuit.

The purification of the neon or the helium will be effected by interposition in the supply-pipe of a tungsten filament brought to a red glow under the same conditions as those indicated above.

I claim:

1. The improved process of manufacturing luminous discharge tubes, comprising the eliminationof the gases occluded'in the electrodes by exposing same to electric discharges in a separate tube lled with nitrogen, regulating the current intensity; mounting the purified electrodes in end branches of the tubes, then fusing said branches to the tubes; purifying the luminous tube thus formed by means of electric discharges in a nitrogen filling with subsequent absorption of residual gases by an auxiliary electrode made of palladium; emptying the tube and filling same with a rare gas previously purified substantially as described.

2. In luminous electric discharge tubes filled with rare gas, the provision at one end of a plurality of substantially indentical electrodes, connected in parallel, and each made of a spirally wound plate of metal having a high melting point, so that the natural differencebetween the electric resistances of the different electrodes will bring an alternation in the electric discharges for the differ ent electrodes.

3. In luminous electric discharge tubes filled With rare gas, the provision at each end of a plurality of substantially identical electrodes, connected in parallel, and each vmade of a spirally wound plate of metal having a high melting point, so that the natural difference between the electric resistances of the different electrodes will bring an alteration in the electric discharges for the different electrodes.

In testimony whereof I signed hereunto i my name. 

